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Light-blue barite from Jebel Ouichane in Morocco forms blade-like tabular crystals (up to ca. 10 cm) with superb transparency and lustre. It represents one of the most spectacular gem-quality specimens in the world. The barite is hosted by iron-ore-bearing skarns, developed within Jurassic-Cretaceous limestones, and occurs in close spatial association with calcite. Although it exhibits simple chemical composition, some irregular sectorial zoning, maintained by elevated contents of Sr in various crystal domains, were found. Barite from Ouichane is abundant in one phase (liquid or gas) or two-phase (liquid-gas) fluid inclusions of primary, pseudosecondary, and secondary origin. A combination of fluid inclusion microthermometry and stable isotope data suggest that δ18O value of barite-forming solutions, resulting from mixing of meteoric waters with hydrothermal fluids, could be in the range from -3,5‰ to +2,7 ‰ (VSMOW), whereas the main barite crystallization stage falls in the temperatures range of 160-180 °C. The recorded first ice melting temperatures (-35.9 to -41.5 ºC) indicate the presence of divalent cations, i.e. Ca2+and Mg2+ in addition to NaCl ± KCl in the mineralizing fluid composition. The possible source of SO42- and Ba2+, which gave rise to the barite formation was fluid enriched in Ba, Sr, Ca, Mg, S, and other elements derived from the alteration of carbonate and silicate minerals, being components of sedimentary and igneous rocks found in the surroundings of Nador area. Necessary amounts of sulphur could be in turn provided by weathering of pyrite and/or decomposition of organosulphur compounds. The combination of δ34S and δ18O values of barite (+16.39‰ and 6.71‰, respectively) indicate that its formation occurred in a steam-heated (near-surface) environment.

Mineralogical and geochemical characteristics of amber deposits located in the Dominican Republic, i.e., Hato Mayor Province of the Eastern Mining District (EMD) in the Cordillera Oriental, and Santiago Province of the Northern Mining District (NMD) in the Cordillera Septentrional were performed. The results of analyses of amber-bearing sediments collected from the borehole in Siete Cañadas area (EMD) were referenced to the petrological data obtained for the coaly shales from La Cumbre (NMD). The mineralogy of the rocks was described using transmitted and reflected light microscopy, scanning electron microscopy, Powder X-ray diffraction and Fourier Transform Raman Spectroscopy. Biomarker analyses by the gas chromatography-mass spectrometry were used to trace the genetic source and transformation stage of abundant organic matter hosted in the core sediments. Our findings indicated that basins in EMD and NMD regions were different isolated palaeosettings, in which under the influence of local physicochemical factors the terrigenous material was transformed and got maturated. In both amber deposits, the sedimentation of clastic and organic material proceeded in the presence of marine conditions. In case of the NMD area, the sedimentation underwent probably in the conditions of the lagoon environment, a shallow maritime lake or periodically flooded plain, that facilitated organic matter decomposition and carbonation from meta-lignite to sub-bituminous coal (random reflectance of coal - Rro = 0,39%). In the EMD region, the sedimentation took place in a deeper basin, where terrigenous material was likely mixed with material found in situ (fauna fossils, carbonate-group minerals) to form the mudstones enriched in bituminous substance of low maturity. The organic matter found in the rocks from both regions is of mixed terrestrial/marine origin and was deposited in the presence of low oxygen concentration and reducing and/or dysoxic conditions.

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